There are many applications where coherent pulses from a laser are required, which can be varied in width and/or repetition rate. For example, coherent laser pulses are useful in optical communications, Lidar (laser radar), optical gyroscopes, and physics instruments. One way for producing such pulses is by mode locking lasers, but the mode locking parameters are not easily changed to control repetition rate or pulse duration. Another technique is the use of a continuous wave laser and a pulsed amplifier, but this has the complication of requiring two lasers. An even simpler apparatus for producing coherent pulses from a single laser, would be of considerable value.